The present invention is related generally to memory cells, and, more particularly, to memory cell arrays used in display systems.
In current memory cell arrays, memory cells in a row of the array are connected to a single wordline for activating the memory cells. For example, in a typical Dynamic Random Access memory (DRAM) cell array as illustrated in FIG. 1, DRAM cells of row 110 are connected to and activated by wordline 112. A critical constraint on this type of design is that, regardless of the user""s intention, the wordline activates all memory cells of the row simultaneously for writing the intended memory cells during a writing cycle. Consequently, the timing of write events is highly correlated. This time-correlation may cause artifacts, such as dynamic-false-contouring (DFC) in display systems that employ memory cell arrays for controlling the pixels of the display systems and pulse-width-modulation (PWM) technique for displaying gray-scales of images.
As a way of example, FIGS. 2a to 2d illustrate the formation of DFC artifacts in the boundary of two neighboring pixels that are controlled by two neighboring memory cells sharing one wordline. Referring to FIG. 2a, pixels 351 and 353 are two neighboring pixels of the display system and are controlled by two neighboring memory cell, such as memory cells 113 and 115 in FIG. 1. Assuming that gray-scaled images of an object traversing from left to right are to be displayed by the two pixels, illumination intensities of the two pixels are modulated using PWM waveforms such that, in the screen (pixel) coordinate, the averaged illumination intensity over a frame duration T of each pixel corresponds to the desired grayscale of the image. As viewed by stationary human eyes, the difference of the averaged illumination intensity at the boundary of the two pixels is perceived as the contour of the object, as shown in FIG. 2b. 
However, the contour of the object will be distorted in the retina coordinate in viewer""s eye when the eyes move with the object. FIG. 2c presents the two pixels in the retina coordinate that moves with the eyes and the object. As can be seen, the pixels are distorted. The boundary of the two pixels is extended into a region, in which the averaged illumination intensity varies with position, as shown in FIG. 2d. This variation of the averaged illumination intensity will be perceived and recognized by the eyes as xe2x80x9crealxe2x80x9d contour of the object. This phenomenon is generally referred to as DFC artifact.
Therefore, methods and apparatus are desired for decorrelating the memory cells and associated pixels of a spatial light modulator such that the DFC like artifacts can be effectively reduced, if not removable.
In view of the foregoing, the present invention provides a method for operating memory cells in each row of the memory cell arrays such that the update events of neighboring memory cells are decorrelated in time. The pixels corresponding to the memory cells are also time-decorrelated thereby. As a benefit of the present invention, stored voltage states of the memory cells of the memory cell array can be read.
In an embodiment of the invention, a method is disclosed herein. The method comprises: providing a memory-cell array comprising a plurality of memory cells; and activating the memory cells of a row of the array using a plurality of separate word lines of the row such that at least two memory cells of the row are activated by separate word lines.
In another embodiment of the invention, a method for displaying a gray-scale image is disclosed herein. The method comprises: providing a spatial light modulator comprising an array of pixel elements; defining at least a first and a second waveform format based on a pulse-width-modulation technique; defining at least a first set of waveforms according to the first waveform format and the gray scale of the image; defining at least a second set of waveforms according to at least the second waveform format; updating the pixels of a row of the array in accordance with a plurality of waveforms that are selected from the first and second sets of waveforms such that at least a first pixel of the row is written in accordance with at least a first waveform selected from the first set of waveforms, and at least a second pixel other than the first pixel of the row is written in accordance with at least a second waveform selected from the second set of waveforms.
In yet another embodiment of the invention, a system is provided herein. The system comprises: a memory-cell array comprising a plurality of memory cells; and a plurality of word-lines coupled to the memory cells of a row of the memory-cell array for selectively activating the memory cells such that at least two memory cells of the row are coupled to separate word-lines of the plurality of word-lines.
In a further embodiment of the invention, a display system for displaying a gray-scale image on a target is proved herein. The display system comprises: a light source; a spatial light modulator that employs a pulse-width-modulation technique for displaying the image by reflecting a beam of incident light from the light source and selectively directing the reflected light to the target, the spatial light modulator further comprising: a plurality of micromirrors for selectively reflecting the beam of incident light onto the target; a memory-cell array having a plurality of memory cells for storing a set of information for controlling the deflections of the micromirrors; and a plurality of word lines coupled with the memory cells of a row of the memory-cell array for activating the memory cells for updating the stored information such that at least two different memory cells of the row can be actuated by separate word lines of the plurality of word lines.
In still a further embodiment of the invention, a method for displaying a gray-scale image on a target is disclosed herein. The method comprises: defining a set of separate waveforms in accordance with at least a gray-scale information of the image and based on a pulse-width-modulation technique; directing an incident light onto a micromirror array that has a plurality of deflectable reflective micromirrors; and selectively reflecting, by the micromirror array, the incident light onto the target according to the set of separate waveforms such that at least two different micromirrors of a row of the array reflect the incident light according to at least two separate waveforms.
In yet another embodiment of the invention, a method for displaying an image is disclosed herein. The method comprises: providing a spatial light modulator having rows and columns of pixels in an array; addressing pixels within a row of the array by providing a brightness level to each pixel in the row, the brightness level being achieved by activating each pixel with a series of bits of varying different lengths, wherein the combination of xe2x80x9conxe2x80x9d bits during a frame corresponds to a brightness level for each pixel; and wherein the order of the series of bits for each pixel in a row is not the same or the weightings of the series of bits are different.
In still yet another embodiment of the invention, a method for displaying an image is disclosed herein. The method comprises: providing a spatial light modulator having rows and columns of pixels in an array; addressing pixels within a row of the array by providing a brightness level to each pixel in the row, the brightness level being achieved by activating each pixel with a series of bits of different lengths, wherein a plurality of pixels in the row have the same brightness level but a different combination of xe2x80x9conxe2x80x9d and xe2x80x9coffxe2x80x9d bits during a frame.
In yet another embodiment of the invention, a spatial light modulator is provided herein. The spatial light modulator comprises: a plurality of rows and columns of pixels in an array; a bit line for each column; and a plurality of word lines for a row of the plurality of rows.
In a further embodiment of the invention, a method for reading voltage states of the memory cells of the memory cell array used of a spatial light modulator is disclosed herein. The method comprises: providing a spatial light modulator that further comprises a memory cell array, the array comprising a reference row, and each row of the array being connected to a plurality of wordlines; reading a voltage state of a memory cell of a memory-cell array, further comprising: selecting a reference cell from the reference row, wherein the selected reference cell being connected to a wordline different from a wordline connecting a reference cell that is connected to the same bitline as the memory cell being read; setting the selected reference cell to a predefined voltage; activating the memory cell being read; activating the selected reference cell; measuring a reference voltage signal from the bitline connecting the selected reference cell and a voltage signal from a bitline connecting the memory cell being read; comparing the reference voltage signal and the voltage signal; determining the voltage state of the memory cell based on the comparison.
In another embodiment of the invention, a system is provided herein. The system comprises: a memory cell array comprising a plurality of memory cells; a first and second sets of wordlines connected to the memory cells for activating the memory cells; wherein at least two memory cells of each row of the memory cell array are connected to at least two separate wordlines selected from the first and second sets of wordlines; wherein the memory cells connecting the first set of wordlines are connected to a first set of bitlines; and wherein the memory cells connecting the second set of wordlines are connected to a second set of bitlines; a row of reference memory cells comprising a plurality of reference memory cells, wherein at least two reference memory cells are respectively connected to two separate wordlines selected from first and second sets of wordlines; and wherein the reference memory cells connected to the wordline of the first set of wordlines are connected to the first set of bitlines; and wherein the reference memory cells connected to the wordline of the second set of wordlines are connected to the second set of bitlines; a plurality of electrodes, each of which is connected to one of the memory cells of the memory cell array such that the voltage of the electrode is determined by the voltage maintained by the connected memory cell; and a plurality of micromirrors, each of which is electrostatically controlled by one of the plurality of electrodes.